The congruent angles formed by the intersection of two lines and are opposite to each other are called verticle angles.
Two lines are intersect each other and form four angles in which, the angles that are opposite to each other are verticle angles. These opposite angles (verticle angles ) will be equal.
A o = C o
B o = D o
If the angle A is 40 degree, then find the other three angles.
A= 40 deg
Vertical angle and remaining two angles
A = C ,
Therefore, C = 40
B = 180-A = 140
B = D ,
Therefore, D = 140